Doc: Some prostate drugs nix blood donation

Dear Dr. Roach: Is there anything that I could take for an enlarged prostate that would allow me to donate blood? I have been trying saw palmetto and pygeum. Thank you.

M.J.C.

Dear M.J.C.: One class of medicines used to treat an enlarged prostate is called the 5-alpha reductase inhibitors. These work by blocking a type of testosterone called dihydrotestosterone, a substance that promotes both enlargement of the prostate and hair loss. These medicines, finasteride (Proscar) and dutasteride (Avodart), are used to treat male pattern baldness and benign (not cancerous) enlargement of the prostate. Saw palmetto works the same way, although it is not nearly as potent as the prescription medications. Pygeum is thought to work primarily as an anti-inflammatory, but it also may block dihydrotestosterone.

Because dihydrotestosterone is necessary for normal development of boys while in the uterus, these medications are likely to cause birth defects in boys, even at very low doses, so blood banks don’t want to take the chance that your blood might be given to a pregnant woman. I’m specifically referring to the prescription medications.

Men treating their prostate problems with alpha blockers, such as tamsulosin (Flomax), can safely donate blood.

There are several other drugs that cannot be taken by people giving blood. A list, courtesy of the Mayo Clinic, with the reasons for why they cannot be used by blood donors and the length of time they need to be stopped prior to donation, can be found at tinyurl.com/blood-drug.

Dear Dr. Roach: Let’s say I get 10 blood samples taken at the same time for cholesterol, or one sample split into 10. I’m curious how much variability in results would come from the test procedure itself, since my blood sample cholesterol level is (theoretically) identical.

P.P.

Dear P.P.: “Reliability” is the engineering term for the ability of a test to give the same result for the same sample. The reliability of a modern commercial laboratory analyzer is very, very good, on the order of 1 percent. So, the 10 blood samples all should be close.

However, in a given person, the results can vary much more than 1 percent, even over a short period of time. I found studies showing that the (fasting) blood cholesterol results could change by 8 percent over one week, and 20 percent over four weeks. When laboratory results vary from one test to another, the vast majority of the difference is likely to be due to changes in the person, not the laboratory, at least for common blood tests.

A 1 percent error from test to test is very good for cholesterol, but there are tests where a 1 percent error can mean a big difference in a person’s treatment. In the case of bone density scanning, the test reliability error is high enough that sometimes, clinically, we have to evaluate a trend using several points of measurement, since 1 percent is an enormous difference in bones. They change slowly.

Because of individual variation of laboratory results, it often is wise to recheck results before acting upon them.